> Or they add something that detects your legitimate disc and lets you play it. I don't> believe the readable portion in Xbox discs is the same across all discs, so I think> this could be a plausible workaround.

They may be able to use them as key discs. However it would be trivial to fake that. Then they are not only letting you have the game for free, but they are paying for bandwidth and hosting.

They only do it on games consoles to tempt people from buying into PlayStation. The only reason I could see them doing it for PC would be to get you into paying for a subscription service. Where the cost will end up being higher than if you buy the xbox and games second hand.